Precise Point Positioning

(PPP) Technique versus

Network-RTK GNSS

Reha M. Alkan1,2, İ.M. Ozulu1 and V. İlçi1

1 Hitit University, Çorum, Turkey2 Istanbul Technical University, Istanbul, Turkey

Introduction

Motivation

Aplication - Kinematic Test

Evaluation of the Measurements

Conclusion

Major developments in the world of informatics have led to the

development of different solutions with various algorithms, and

major changes in numerous professional fields as well as in

satellite-based positioning.

Introduction

Although; in the 1990’s, it was necessary to obtain

positioning with Global Positioning Systems (GPS) using at

least two receivers; nowadays an accuracy of within a

centimetre level of positioning has become possible using a

single receiver data with advanced techniques.

One of which is Network-RTK used extensively in the world,

producing economical and rapid solutions for the users

7/24/365.

According to the results obtained the Network-RTK has been

used quite widely all over the world due to it many advantages

like;

- accurate and fast positioning,

- easily be used by one person,

- cost-effective.

On the other hand, it has some restrictions and this limits its

usage in some cases and remote places.

The most important restriction is; this technique, similar to

all of the differential techniques, needs additional data, i.e.

correction, from at least one reference station and the

distance between the rover and its reference station is not un-

limited (should be about 50-100 km).

TUSAGA-AKTIF Reference Stations in TURKEY

The network consists of 146

reference stations with an average

spacing of 70-100 km covering the

entire country.

provides few cm-level of accuracy even

in a couple of seconds, fast, easy and

cost-effectively, 365/24/7 in real-time.

Over the past decade, researchers have made studies to

develop more economical, convenient, reliable, and worldwide

precise positioning solutions, which do not have the

disadvantages that exist in the conventional differential

GNSS techniques, including CORS-like.

In this frame, one of the commonly used methods is Precise

Point Positioning (PPP).

PPP provides positioning without the need for a reference station

using a stand-alone GNSS receiver by using precise satellite

orbit and clock corrections.

With this method, it

has become possible

to reach a cm to dm

level of positional

accuracy in the static

or kinematic mode.

The user of this method can obtain his/her position;

within a global reference frame,

anywhere in the world easily,

economically,

without any need of a base station data

offers great operational flexibility.

The use of PPP has been increased, but it has some drawbacks

including necessity of long occupation time for converge and

unavailability of PPP processing mode in common commercial

GPS processing software.

Especially long convergence time is limited its use in many

situations where rapid GPS surveying is required and surveying

efficiency is concerned.

There is a number of software packages to estimate PPP-

derived coordinates, i.e.,

- individuals at universities or research organizations,

- scientific GPS processing software and,

- in recent years, web-based on-line processing

services.

The use of the processing services has become widely popular

because of their ease of use, being free of charge (or requiring low

cost fee) and no requirement of a license and knowledge of a GPS

processing software.

In these services, users can

upload/send their GPS

observation file(s) which will

be processed automatically

and estimate the coordinates (or trajectory).

In this study Canadian Spatial Reference System-Precise

Point Positioning Service (CSRS-PPP) operated by Geodetic

Survey Division of Natural Resources Canada (NRCan) online

service was used to obtain PPP-derived coordinates.

from http://www.novatel.com

In this study, we aim to make an accuracy comparison of

the Network-RTK and the PPP techniques in a dynamic

environment.

Aplication - Kinematic Test

In order to compare the TUSAGA-Aktif Service and PPP

technique in terms of accuracy in a dynamic environment, a

kinematic test was conducted at the Obruk Lake Dam, in

Çorum, Turkey in October of 2015.

The kinematic part of the study was started with static initialization for

a short time and the receiver was then moved to the vessel and data

was collected for approximately 1.5 hours at 1-second interval with an

elevation mask of 10°

While the kinematic test was lasting, another receiver was

occupied on a known point at the shore and GPS data was

collected in static mode.

The precise coordinates (or reference trajectory) of the

vessel for each epoch with the differential (relative) GNSS

method using both the GNSS data collected to the vessel

and at the reference station on the shore.

In this test study, ProFlex 500 GNSS receivers with

geodetic–grade antenna was used.

ProFlex 500 is a 75 channel (GPS L1 C/A L1/L2 P-code,

L2C, L1/L2; GLONASS L1 C/A, L2 C/A code, L1/L2) receiver

with having up to 20 Hz of raw data and position output.

While the kinematic measurement was lasting, the Network-

RTK coordinates were recorded simultaneously for each

measurement epoch in real-time from the nearest TUSAGA-

Aktif Network’s point.

The collected data from the vessel was sent to the CSRS-

PPP service the day after the data collection date, using the

service’s interactive web page by choosing the kinematic

processing option.

The kinematic PPP coordinates for each measurement epoch

with solution reports were retrieved a short time later via e-

mail from the service.

Evaluation of the Measurements

The coordinates of the vessel determined with the TUSAGA-

Aktif Network and NRCan’s CSRS-PPP online service were

compared with those of differential solution of the LGO

software, i.e. to the reference coordinates, epoch-by-epoch.

Differences between Known-coordinates (Differential Solution) and NRCan’s CSRS-PPP &

TUSAGA-Aktif Network

blue line; CSRS-PPP, red line: CORS or TUSAGA-Aktif Network

Statistical Comparison of the Results

The results of the test measurement show that,

the Network-RTK provides a cm level of accuracy when the

solution can be fixed. Otherwise, the accuracy decreases

dramatically to even a meter-level of accuracy if the

float/DGPS solution occurs due to problems in the

communication link, outside the coverage area of the GSM

network or where the absence of data transmission is poor.

Conclusions and Results

Concerning the PPP technique, the kinematic test results

showed that the PPP-derived coordinates converge to the

relative solutions with a couple of cm-level of accuracy. This

accuracy has allowed the technique to be a viable

alternative to conventional differential GNSS techniques in

terms of accuracy, easy-use and cost-effectiveness while

reducing labour and equipment costs.

Conclusions and Results

Although Network-RTK offers many advantages over

conventional differential GNSS techniques, PPP techniques

needs a single receiver and this removes the necessity for

the base (reference) station(s) or data from the CORS-like

networks. Thus PPP is still useful in areas that are not

covered by CORS infrastructure due to low population

density, economic reasons, or operational constrains.

Conclusions and Results

Hoping to see you in İstanbul for FIG 2018

Thank you very much for your

interest and attention…

Contributions, Questions???

Prof.Dr. Reha Metin ALKAN

Hitit University, Corum, Turkey & Istanbul Technical University, Istanbul, Turkey

alkan@hitit.edu.tr